A thank you to billy liar@Flickr (starter of the Flickr “Fat Plants” group) for sharing today’s photograph (BPotD Flickr Group Pool | original image). Much appreciated!
The simplest name to apply to this plant is the common one: rainbow hedgehog cactus. I made an attempt to figure out the most recent accepted scientific name and had to abandon it. “billy liar” stated this plant’s name was Echinocereus rigidissimus var. rubrispinus (the varietal epithet meaning red-spined), but when checking the nomenclature, I ran into a few problems. The USDA Plants Database entry on Echinocereus rigidissimus doesn’t subdivide the species into subspecies or varieties. However, the distribution of this taxon extends from southwest USA into Mexico, so it is quite possible that the variety rubrispinus only occurs in Mexico, and so wouldn’t be covered in the USDA database.
This does seem to be the case after browsing through Echinocereus Online where it lists the taxon Echinocereus pectinatus var. rubispinus as occurring in Chihuahua, Mexico. This reference suggests that Echinocereus rigidissimus var. rubrispinus is an outdated name. However, looking back at the USDA database, it seems those taxonomists would make the opposite conclusion, based on their listing of Echinocereus pectinatus var. rigidissimus as a synonym for Echinocereus rigidissimus. Conclusion? Confused.

this is really beautiful i am so happy to wake up to this image.
This is so intricate in design, and the colours are very seasonal, what a beauty! Its like a huge fragile Christmas bauble, I could never get tired of gazing at it.
I call this the Arizona Rainbow… I collected mine in the hills near Kartchner Caverns. Being subjected to the varying years ( About 4 ) of weather, it is fat in some stages of growth, narrow in others. Kinda looks like a Snowman ! The colors are Red-Pink, some Golden Yellow, and neat violet, and of course vivid Green.. All I need is the Blue ! Anybody wanna see a Pic ?
Must be the smartest plant on this planet as not only can you not track down its name its rays cannot be counted maybe that’s why it has no taxonomic pinhole pigeonhole to inhabit.
One thing we do agree on is that its structure and colour scheme is both ineffably and chaotically beautiful. Should be the emblematic cult flower of anarchists. As long as they spin.